Read the Passage carefully and answer the Questions.
Carbonyl compounds such as aldehydes, ketones, and carboxylic acids play an important role in the biochemical process of plants and animal kingdom. Many aldehydes and ketones find applications in dye, perfumery and other industries. The carbonyl carbon atom is \( sp^2 \)-hybridized forming three sigma and one pi-bond with oxygen. C-O bonds are polar bond due to high electronegativity of oxygen than carbon. Hence the carbonyl carbon behaves as an electrophilic center and oxygen as a nucleophilic centre. Primary and secondary alcohols yield aldehydes and ketones respectively upon oxidation with variety of oxidizing agents. The boiling points of aldehydes and ketones differ from hydrocarbons and ethers. Aldehydes and ketones undergo nucleophilic addition reaction due to presence of electrophilic carbonyl carbon. Nucleophile and a proton add across the carbon oxygen double bond.
Identify the product Y in the following reaction
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → but-2-enal (\( \ce{CH3CH=CHCHO} \))
Primary alcohols are oxidised first to aldehydes and then to carboxylic acids. Strong oxidising agents such as acidified potassium permanganate take the oxidation all the way to the acid. Pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HCl, is a mild reagent: it stops the oxidation at the aldehyde and does not attack a carbon-carbon double bond.
But-2-en-1-ol is a primary alcohol. PCC oxidises only its \( \ce{-CH2OH} \) group to \( \ce{-CHO} \); the double bond is left as it is:
\( \displaystyle \ce{CH3-CH=CH-CH2OH} \xrightarrow{\text{PCC}} \ce{CH3-CH=CH-CHO} \)
So Y is but-2-enal (crotonaldehyde).
Why the other options are incorrect
Option (1) butan-1-ol (\( \ce{CH3CH2CH2CH2OH} \)) — Incorrect. This would need the C=C bond to be reduced, for example with \( \ce{H2} \)/Ni; PCC is an oxidising agent.
Option (3) but-2-enoic acid (\( \ce{CH3CH=CHCOOH} \)) — Incorrect. A strong oxidising agent would take the alcohol on to the acid; PCC does not oxidise the aldehyde further.
Option (4) butanoic acid (\( \ce{CH3CH2CH2COOH} \)) — Incorrect. This would need both the reduction of the double bond and oxidation to the acid; neither happens with PCC.
NCERT (2026-27 edition):
Oxidation – …
